High voltage dual isolated output tracking power supply

ABSTRACT

A cathode ray tube power supply circuit is disclosed which permits the voltage differential between cathode and grid electrodes to be precisely controlled. The circuit includes a floating grid voltage supply, to which blanking and control signals may be applied. A grid analogue circuit, which is identical to the grid voltage supply circuit in all respects, is included to duplicate the behavior of the grid voltage supply circuit. The grid analogue circuit is coupled throug a feedback network to a differential amplifier circuit, which also receives a feedback signal from a cathode voltage supply circuit. The output of the differential amplifier circuit controls a low voltage supply which in turn supplies a component voltage which controls the cathode voltage output. This arrangement causes the cathode voltage supply to vary in the same manner as the grid voltage supply, and accordingly maintains a precise differential between the voltages applied to the cathode and grid.

United States Patent Richards, Jr. et al.

1 June 19, 1973 HIGH VOLTAGE DUAL ISOLATED OUTPUT TRACKING POWER SUPPLY [22] Filed:

Assignee: AMP Incorporated, Harrisburg, Pa.

Apr. 18, 1972 Appl. No.: 245,075

52 us. Cl. 307 55, 315/1 Primary Examiner-William M. Shoop, Jr. Attorney-William J. Keating et al.

[57] ABSTRACT A cathode ray tube power supply circuit is disclosed which permits the voltage differential between cathode and grid electrodes to be precisely controlled. The circuit includes a floating grid voltage supply, to which blanking and control signals may be applied. A grid analogue circuit, which is identical to the grid voltage supply circuit in all respects, is included to duplicate the behavior of the grid voltage supply circuit. The grid Field 0f Search analogue circuit is coupled throug a feedback network /2, 16 to a differential amplifier circuit, which also receives a g feedback signal from a cathode voltage supply circuit.

[ References Cited The output of the differential amplifier circuit controls UNITED STATES PATENTS a low voltage supply which in turn supplies a compo- 2,697,798 12 1954 Schlesinger 315 27 R voltage whlch controls the Wltage 2,932,765 4/1960 Messina 1 315 27 R Put-T1115 arrangement Causes the cathode vvliage P- 3,473,081 10/1969 Yoshikawa 315/30 ply to vary in the same manner as the grid voltage sup- 2,854,592 9/1958 Ruth 315/29 ply, and accordingly maintains a precise differential be- 2,379,445 3/1959 Gordon I 315/22 X tween the voltages applied to the cathode and grid.

2,997,622 8/1961 Claypool 1 315 27 R o 3,077,550 2/1963 Macovski 315 29 x 14 Chums, 1 Drawlng Flgure I 18 ANODE HVRECTIFIER- F MULTIPLIER I2 14 f f 22 0c 01: TO AC Fo'cus SOURCE ncuiJLATOR CONVERTOR Hv REC-PIER.

T] MULTIPLIER GRID HVRECT|F1ER- 28 MULTIPLIER loll-$2165 42 3% CO N T R OL SUPPLY '1 CIRCUIT i CATHODE 3o DIFFERENTIAL HV RECTIFIER 4o- AMPLIFIER MULTIPLIER CIRCUIT I CATHODE 36 f V FEEDBACK FILAMENT CIRCUIT 50 FEEDBACK FILAMENT ANALOG CIRCUIT SUPPLY cIRcuIT 46 CIRCUIT HIGH VOLTAGE DUAL ISOLATED OUTPUT TRACKING POWER SUPPLY BACKGROUND OF THE INVENTION l. Field Of The Invention This invention relates generally to power supply circuits for cathode ray tubes, and more particularly to power supply circuits for maintaining a precise differential between the voltage applied to the cathode and grid of a cathode ray tube.

2. Description Of The Prior Art The difference in potential, or voltage differential, between the cathode and grid electrodes of a cathode ray tube is a critical quantity, since it essentially determines the operating mode of the cathode ray tube. More particularly, the cathode-to-grid voltage essentially determines the current flow through a cathode ray tube, and accordingly determines the intensity or brightness of the image formed at the anode or face of the tube.

A problem exists in controlling the grid-cathode voltage differential, since normally the cathode and grid must be operated at relatively high voltages, i.e., voltages on the order to several kilovolts. Since high voltage sourcesare normally prone to drifting, due to temperature effects, loading, etc., the voltage differential between cathode and grid of previously known systems normally drifts over a range of at least several volts as these systems are operated. In the past, such fluctuations were simply tolerated or ignored, since many systems in which cathode ray tubes were used were not so sensitive that a difference of a few volts in the cathode to grid differential would make a substantial difference in the performance of the system.

However, in some environments, fluctuations of as little as $0.5 volt in the grid-to-cathode potential is highly significant. In such systems, previously available cathode ray tube power supply circuits are entirely in adequate dueto excessive drift in the cathode-t'o-grid voltage differential. For example, in random access display systems, the positioning of an electron beam on a CRT face is very critical, and the intensity of the beam is also very critical. Accordingly, it is extremely important in such systems that the cathode-to-grid voltage differential be maintained as nearly constant as possible.

SUMMARY OF THE INVENTION Accordingly, one object of this invention is to provide a novel power supply for maintaining the cathodeto-grid voltage potential of a cathode ray tube substantially constant.

Another object of this invention is to provide a highly stable power supply for a cathode ray tube.

A still further object of this invention is to provide a novel power supply for a cathode ray tube that maintains the voltage differential between cathode and grid electrodes at a substantially constant value regardless of loading or environmental conditions.

Another object of this invention is to provide a cathode ray tube power supply circuit which is inexpensive to construct and extremely reliable in operation.

Briefly, these and other objects of the invention are achieved by providing a grid voltage supply circuit, and a grid analogue circuit which is identical in all respects to the grid voltage supply circuit. The grid analogue circuit and a cathode voltage supply circuit are coupled through feedback networks to a differential amplifier. The differential amplifier controls a low voltage power supply in response to a comparison of the two feedback signals. The low voltage supply adjusts the magnitude of the cathode voltage supply in such a manner as to maintain the difference between the cathode and grid voltages at a fixed magnitude.

BRIEF DESCRIPTION OF THE DRAWING A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

The FIGURE is a block diagram of the cathode ray tube power supply circuit of the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, a preferred embodiment of the power supply circuit of the present inven tion is illustrated in block diagram form. A DC power source 10, which may be on the order of volts for example, is provided as a power source for the circuit of the present invention. The output of the DC source 10 is coupled to a voltage regulator 12 which regulates or reduces fluctuations in the magnitude of the voltage emanating from the DC voltage source 10. This arrangment permits the overall system to operate with reasonably good accuracy even though the DC voltage souce should fluctuate as much as a :10 volts. The output of the regulator circuit 12 is fed to a DC-to-AC converter 14. The DC-to-AC converter 14 may be a conventional Royer circuit, for example, including a self-saturating transformer. As is known to those skilled in the art, such a circuit may include a pair of transistors oscillating in a push-pull mode. That is, the circuit arrangement is such that one transistor conducts until the transformer becomes saturated in one direction, which causes biasing voltage to be removed from the first transistor and applied to the second transistor. Thus the first transistor then becomes non-conductive and the second transistor becomes conductive until the transformer is saturated in the opposite direction. This oscillating process continues indefinitely, causing a DC input voltage to be converted to an AC output voltage.

The output of the DC-to-AC converter 14 is applied to a plurality of high voltage rectifier-multiplier circuits, which apply suitable voltages to the various electrodes of a cathode ray tube 16. For example, an anode high voltage rectifier-multiplier 18 is coupled to, and applies a suitable potential to, an anode electrode 20 of the cathode ray tube 16. The anode voltage may be on the order of +4.5kv, for example. Similarly, a focus high voltage rectifier-multipler 22 is coupled to a focus electrode 24 of the cathode ray tube 16 for supplying a suitable focusing potential. The focusing potential may be on the order of2.6kv, for example. The focus high voltage rectifier-multiplier 22 is a floating power supply, which is not directly referenced to a ground po tential. However, a focus control input'26 is coupled to the focus high voltage rectifier-multipler 22 to adjust the relative output voltage thereof, and thereby to adjust the focus of the cathode ray tube beam. The focus input voltage applied at the terminal 26 is referenced to ground.

A grid high voltage rectifier-multiplier 28 is also coupled to the DC-to-AC converter 14 at its input, and is coupled to a grid electrode 30 of cathode ray tube 16. The grid high voltage rectifier-multiplier (or grid voltage supply) is also a floating voltage supply in that it is not directly referenced to ground potential. A grid control circuit 32, which is coupled to the grid voltage supply 28, supplies a variable reference potential to the grid voltage supply circuit. Thus, by adjusting the output of the grid voltage control circuit, the relative potential of the grid high voltage rectifier-multiplier may be adjusted. Accordingly, the relative voltage applied to the grid electrode 30 may be adjusted to the quiescent potential of the cathode ray tube 16. The return 33 of the grid control circuit is floating, and may be connected to a DC. amplifier as will be explained.

The normal output voltage of the grid high voltage rectifier-multiplier 28 may be on the order of 3.075 kv, for example. This voltage is changed, or adjusted, by the output of the grid control circuit 32 to any suitable value or voltage level.

A filament supply circuit 34 is also coupled to the DC-to-AC converter 14 at its input, and to a filament electrode 36 of the cathode ray tube 16 at its output. The filament supply is referenced to the cathode potential.

Similarly, a cathode high voltage rectifier-multiplier or cathode voltage supply 38 is coupled to the output of the DC-to-AC converter-l4. The output of the cathode high voltage rectifier-multiplier 38 is coupled to a cathode electrode 40 of the cathode ray tube 16. The cathode voltage supply 38 is a floating voltage supply which has a nominal output voltage on the order of 3kv, for example. As pointed out above, the cathode high voltage rectifier-multiplier 38 is a floating voltage supply, and is therefore not referenced directly to ground potential. Instead, a low voltage supply, having a nominal output magnitude on the order of 100 volts for example, provides a voltage for control of the oathode voltage output 40,,as will be explained hereinafter. The low voltage supply 42 is coupled to the DC-to-AC converter 14. its output is coupled to the reference input of the cathode high voltage rectifier-multiplier -A grid analogue circuit 44 is also coupled at its input to the DC-to-AC converter 14. The grid analogue circuit 44 is essentially an exact duplicate of the grid high voltage rectifier-multiplier 28. Extreme care is taken in assembling the grid high voltage rectifier-multiplier 28 and the grid analogue circuit 44 to insure that they are identical inall respects. Thus, the time constants, capacitance, temperature dependence, and each component of the two circuits are made identical. In addition, care is taken to insure that the output windings of the DC-to-AC converter 14 which drive the circuits 28 and 44 are also identical in all respects, so that the input voltage applied to the circuits 28 and 44 is always identical. Thus, since the grid analogue circuit 44 is identical in all respects to the grid high voltage rectifiermultiplier 28, the output of the grid analogue circuit 44 is exactly the same as the output of the grid high voltage rectifier multiplier, provided the control input to the grid high voltage rectifier-multiplier is grounded. Accordingly, the output of the grid analogue circuit 44 behaves in precisely the same manner as the output of the grid high voltage rectifier-multiplier 28. Thus, the grid analogue circuit 44 provides an accurate indication of any changeswhich occur in the output of the grid high voltage rectifier-multiplier 28. The grid analogue circuit 44 is referenced to ground.

The output of the grid analogue circuit 44 is coupled through a feedback circuit 46 to a differential amplifier circuit 48. The feedback circuit 48 includes a voltage divider, so that the signal applied to the differential amplifier circuit 48 is of a relatively low magnitude, such as 40 volts, for example. A similar feedback circuit 50 is coupled between the output of the cathode high voltage rectifier-multiplier 38 and the differential amplifier circuit 48. The differential amplifier circuit 48 is coupled at its output to the low voltage power supply 42, and serves to control the output voltage level of the low voltage supply 42. Thus, the differential amplifier circuit 48 compares the feedback signals applied through the feedback circuits 46 and .50, and generates an output signal in response to the relative magnitudes of the two feedback signals in order to adjust the output voltage of the low voltage supply 42.

Thus in operation, a desirable voltage differential is first established between the grid electrode 30 and the cathode 40. This differential may be volts, for example. However, as the complete power supply changes conditions, for example, by heating up, its output voltage may change somewhat, tending to alter the voltage differential between the grid electrode 30 and the cathode electrode 40. However, the grid analogue circuit 44, which isidentical to the grid high voltage rectifiermultiplier 28, will behave in the same manner as the grid high voltage rectifier-multiplier 2 8, and thus its output will change in the same manner as that of the grid high voltage rectifier-multiplier 28. The changing voltage of the grid analogue circuit 44 will be applied through the feedback circuit 46 to the differential amplifier circuit 48. The differential amplifier circuit 48 will in turn generate an appropriate output to adjust the low voltage supply 42. The low'voltage supply 42 will therefore apply an adjusted voltage to the cathode high voltage rectifier-multiplier 38 so as to maintain the differential between the grid electrode 30 and the cathode electrode 40 at precisely its prescribed value. Thus for example, if the grid high voltage rectifier-multiplier 28 begins to generate a higher than normal output voltage, the grid analogue circuit 44 will also generate a higher than normal voltage. This will cause the output of the low voltage supply 42 to be increased, thereby raising the level of the output of the cathode high voltage rectifier-multiplier 38, causing the voltage applied to the cathode electrode 40 to be raised somewhat. The net effect, then, will be to maintain the voltage differential between the grid and cathode electrodes at a constant value.

Similarly, if the output potential of the cathode high voltage rectifier-multiplier 38 should change, due to loading etc., the feedback signal passing through the feedback circuit 50 and the differential amplifier 48 will appropriately adjust the low voltage supply 42 to maintain a constant voltage differential between the grid and cathode electrodes of the cathode ray tube 16.

It will be observed by those skilled in the art, however, that adjustment of the output of the grid high voltage rectifier-multiplier 28 by varying the output signal of the grid control circuit 32 does not influence the grid analogue circuit 44 or the low voltage supply 42. Accordingly, dynamic signals can be applied to the grid electrode through the return 33 of the grid control circuit 32 without in any way effecting the above described feedback network. Thus, the circuit of the present invention maintains the quiescent voltage differential between the grid and cathode electrodes of a CRT with great accuracy, without interfering with the application of dynamic signals to the grid electrode.

For example a D.C. amplifier coupled to the return 33 will produce a dynamic signal on the CRT of an intensity corresponding to the level of the D.C. signal supplied by the amplifier. When two or more signals of different levels are supplied, the corresponding CRT signals will be of different intensities, thereby serving as a voltage comparator, which may be useful, for example, in determining range of detected aircraft. The complete regulator circuit of the invention allows the D.C. amplifier to operate with direct reference to ground without the need for coupling with the CRT circuit through a capacitive step-up circuit. The invention thus allows direct D.C. coupled operation.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. Itis therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Accordingly, what is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A high voltage power supply for a device having first, second and third electrodes at normally different potentials, comprising,

a. means for applying a potential to said first electrode;

b. means for applying a potential different from said first potential to said second electrode;

c. means for providing an analog of said potential applied to said second electrode; and

d. means responsive to the difference of potential provided in (c) and said potential provided in (a) to control said potential provided in (a), whereby the potential difference between said first electrode and said second electrode is maintained constant.

2. A high voltage power supply as set forth in claim 1 further including means reference to a reference potential for applying a potential to said third electrode, said means in (a) and (b) having a floating reference potential.

3. A high voltage power supply as set forth in claim 2 wherein said device is a cathode ray tube, said third electrode is an anode and said first and second electrodes are a grid and a cathode of said tube.

4. A high voltage power supply as set forth in claim 1 wherein, said means responsive to the difference of potential includes a differential amplifier responsive to (a) and '(c), to provide a different signal indicative of the difference and means responsive to said difference signal to control said potential provided in (a).

5. A high voltage power supply as set forth in claim 2 wherein said means responsive to the difference of potential includes a differential amplifier responsive to (a) and (c) to provide a difference signal indicative of the difference and means responsive to said difference signal to control said potential provided in (a).

6. A high voltage power supply as set forth in claim 3 wherein said means responsive to the difference of potential includes a differential amplifier responsive to (a) and (c) to provide a difference signal indicative of the difference and means responsive to said difference signal to control said potential provided in (a).

7. A high voltage power supply as set forth in claim 2 wherein said first electrode is a cathode and said second electrode is a grid.

8. A high voltage power supply as set forth in claim 3 wherein said first electrode is a cathode and said second electrode is a grid.

9. A high voltage power supply as set forth in claim 5 wherein said first electrode is a cathode and said second electrode is a grid.

10. A high voltage power supply as set forth in claim 6 wherein said first electrode is a cathode and said second electrode is a grid.

11. A high voltage power supply for a cathode ray tube having an anode electrode, a cathode electrode and a grid electrode, which comprises a. a source of reference voltage,

b. means referenced to said source of reference voltage to provide a predetermined potential to said anode,

c. means for providing a predetermined potential to said grid,

d. means for providing a predetermined potential to said cathode, and

e. means for maintaining a constant quiescent potential difference between said grid and cathode.

12. A high voltage power supply as set forth in claim 11 wherein said grid and said cathode are electrically isolated from said anode.

13. A high voltage power supply as set forth in claim 11 wherein (e) includes means electrically isolated from said grid for providing an analog of the potential at said grid and differential means responsive to said analog and the potential at said cathode for controlling the potential at said cathode.

14. A high voltage power supply as set forth in claim 12 wherein (e) includes means electrically isolated from said grid for providing an analog of the potential at said grid and differential means responsive to said analog and the potential at said cathode for controlling the potential at said cathode. 

1. A high voltage power supply for a device having first, second and third electrodes at normally different potentials, comprising, a. means for applying a potential to said first electrode; b. means for applying a potential different from said first potential to said second electrode; c. means for providing an analog of said potential applied to said second electrode; and d. means responsive to the difference of potential provided in (c) and said potential provided in (a) to control said potential provided in (a), whereby the potential difference between said first electrode and said second electrode is maintained constant.
 2. A high voltage power supply as set forth in claim 1 further including means reference to a reference potential for applying a potential to said third electrode, said means in (a) and (b) having a floating reference potential.
 3. A high voltage power supply as set forth in claim 2 wherein said device is a cathode ray tube, said third electrode is an anode and said first and second electrodes are a grid and a cathode of said tube.
 4. A high voltage power supply as set forth in claim 1 wherein said means responsive to the difference of potential includes a differential amplifier responsive to (a) and (c) to provide a different signal indicative of the difference and means responsive to said difference signal to control said potential provided in (a).
 5. A high voltage power supply as set forth in claim 2 wherein said means responsive to the difference of potential includes a differential amplifier responsive to (a) and (c) to provide a difference signal indicative of the difference and means responsive to said difference signal to control said potential provided in (a).
 6. A high voltage power supply as set forth in claim 3 wherein said means responsive to the difference of potential includes a differential amplifier responsive to (a) and (c) to provide a difference signal indicative of the difference and means responsive to said difference signal to control said potential provided in (a).
 7. A high voltage power supply as set forth in claim 2 wherein said first electrode is a cathode and said second electrode is a grid.
 8. A high voltage power supply as set forth in claim 3 wherein said first electrode is a cathode and said second electrode is a grid.
 9. A high voltage power supply as set forth in claim 5 wherein said first electrode is a cathode and said second electrode is a grid.
 10. A high voltage power supply as set forth in claim 6 wherein said first electrode is a cathode and said second electrode is a grid.
 11. A high voltage power supply for a cathode ray tube having an anode electrode, a cathode electrode and a grid electrode, which comprises a. a source of reference voltage, b. means referenced to said source of reference voltage to provide a predetermined potential to said anode, c. means for providing a predetermined potenTial to said grid, d. means for providing a predetermined potential to said cathode, and e. means for maintaining a constant quiescent potential difference between said grid and cathode.
 12. A high voltage power supply as set forth in claim 11 wherein said grid and said cathode are electrically isolated from said anode.
 13. A high voltage power supply as set forth in claim 11 wherein (e) includes means electrically isolated from said grid for providing an analog of the potential at said grid and differential means responsive to said analog and the potential at said cathode for controlling the potential at said cathode.
 14. A high voltage power supply as set forth in claim 12 wherein (e) includes means electrically isolated from said grid for providing an analog of the potential at said grid and differential means responsive to said analog and the potential at said cathode for controlling the potential at said cathode. 